1. Field of the Invention
The present invention relates to a cathode and a preparation thereof and an electrolysis using the cathode. More particularly, it relates to a gas evolution cathode having high durability.
2. Description of the Prior Art
The gas evolution cathode has been industrially used as a cathode in an apparatus for electrolysis of an aqueous solution of an alkali metal chloride, sea water (brine), water or hydrochloric acid. Various apparatuses equipped with the cathode have been considered. Thus, an apparatus comprising a liquid permeable or liquid non-permeable diaphragm between an anode compartment having an anode and a cathode compartment having a cathode has been usually used.
An electrolysis of an aqueous solution of an alkali metal chloride especially an ion-exchange membrane type electrolysis of a brine will be illustrated.
An aqueous solution of sodium chloride (a brine) as an electrolyte solution is fed into the anode compartment and water or a dilute aqueous solution of sodium hydroxide is fed into the cathode compartment. As a result of the electrolysis, hydrogen evolves on the cathode and chlorine evolves on the anode. It has been well-known when such gas evolution cathode is used, iron-containing ions such as HFeO.sub.2.sup.- formed by dissolving the cell material etc. in an aqueous solution of sodium hydroxide as a catholyte is reduced into Fe or iron oxides which is deposited on the cathode. It is considered that a reduction rate or an electrodeposition rate is increased on the gas evolution cathode by the electrolyte-stirring effect resulted by the gas evolution.
As a cathode used for such electrolysis and a preparation thereof, the inventors have proposed the cathode obtained by electrolytic codeposition of electrochemically active particles made of Raney nickel etc. with nickel etc. on a cathode substrate as Japanese Unexamined Patent Publication No. 112785/1979 and a preparation thereof. The resulting cathode has been a cathode for remarkably low hydrogen overvoltage in comparison with the known cathodes. However, it has been found that the hydrogen overvoltage of the cathode gradually rises in a system containing iron-containing ions at a content of several ppm or more. Moreover, the deposition of iron or iron oxide on the cathode has been found. According to various studies of the reason, it has been found that an iron component of the iron-containing ions in the catholyte is deposited on the cathode as a water insoluble solid such as iron, iron oxide or iron hydroxide.